Order-disorder transformations in ferromagnetic binary alloys

Abstract

Order-disorder transformations in binary body-centered-cubic alloys with two ferromagnetic components are studied within the mean-field approximation. Only pairwise interactions between nearest neighbors are included. Special attention is given to the temperature dependence of the specific heat in several kind of alloys and discontinuities of the specific heat at the critical temperatures are calculated. Three different situations are analyzed; i.e., (i) ${\Theta }_0 (\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{o}\mathrm{r}\mathrm{d}\mathrm{e}\mathrm{r}-\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{d}\mathrm{e}\mathrm{r}\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l}\mathrm{t}\mathrm{e}\mathrm{m}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e})<\mathrm{}{\Theta }_M \left(\mathrm{Curie}\mathrm{temperature}\right)$, (ii) ${\Theta }_M<{\Theta }_0$, and (iii) $J_{\mathrm{AB}}\ll J_{\mathrm{AA}}$, $J_{\mathrm{BB}}$ where $J_{\mathrm{IJ}}$ are the Ising exchange integrals for the alloy $A_x{B}_{1-x}$ with spins $S_A$ and $S_B$. The Fe-Co system is studied within this model, and the results are compared with experimental data.